The efficiency of resource allocation and the quality of service provided by packet switching networks depends upon effective traffic engineering. Over the years, switched circuit network traffic engineering has become a well known art comprising the steps of measuring traffic over switched circuits in the form of conversation seconds and numbers of calls over periods of time, applying the results to certain probabilistically determined tables, and then installing appropriate facilitates and resources in the switched circuit network to match the measured and expected demand.
Estimating the expected demand, however, is made more difficult when bandwidth is provisioned by Virtual Circuits (VCs) rather than by physical circuits. This is because it is possible for VCs to throw more traffic into the network than what was contracted for with the users. The contracted rate between a user and a frame relay service provider is known as the Committed Information Rate (CIR). The CIR is the level of data traffic that the carrier agrees to handle over a period of time measured in bits per second. Typically, a user identifies to the frame relay provider the particular sites that the user wants to interconnect. Between each of these sites and based on agreement with the frame relay service provider, a Permanent Virtual Circuit (PVC) is established. For each PVC, a path is established across which all data will flow between those sites. The path may be defined when the PVC is added to the network, or computed by the network using a routing algorithm may determine the path. All frames transmitted between the identified sites follow the same PVC path, ensuring that the frames will not arrive out of sequence.
The CIR can be anywhere between 0% and 100% of the speed of the access line and the speed of the port on the device. The offered load to the network can burst above the CIR for a measured period of time. Bust levels are measured as Committed Burst Size, Bc, and Excess Burst Size, Be. Bc is the maximum amount of data per second, measured in bits that the carrier agrees to transfer under normal circumstances. Be is the maximum amount of additional data measure in bits that the carrier will attempt to handle, assuming that congestion conditions in the network permit. Indication of whether the data on the network from the PVCs exceed the Bc or the Be values is designated at the ingress switch where the traffic enters the network and is used by the switches along the path which carry many VCs on a common backbone.
In ATM switches, the excess frames at the Be level are designated as Discard Eligible, (DE) when converted from frames to cells. Through a mechanism known as the Graceful Discard, (GD), the DE cells are forwarded into the network and are discarded, when necessary, by the carrier somewhere in the network during periods of congestion. If the network is not congested, the carrier will deliver the excess frames and bits. For example, one can burst above the CIR to the level of Bc with reasonable assurance that the data will get to the destination site. One can burst above the Bc level, although all bits in the Bc area are subject to being designated DE. The DE bits are discarded in the event that the network is congested and the buffers in the network switches and router overflow. Additionally, one can also transmit above the total of the Bc+Be level, but those bits in those frames may be discarded at a switch along the path.
In Frame switches, all traffic up to the CIR is conforming and is designated as “green”. Traffic from the Bc level up to the Bc+Be level is designated as “amber”, and any subsequent traffic above Bc+Be, is designated as “red”. During periods of congestion, the switch first discards red designated data, then amber designated data, and finally green designated data. If the network is not congested, the carrier will deliver the excess data bits. Any bits designated red, above the Bc+Be level, will be discarded first. Next, if the congestion grows more severe then the amber frames will be discarded. Finally, the green frames will only be discarded if the congestion becomes very severe.
With the number of PVCs on the various networks, the increase in PVC utilization above the contracted rate can lead to a number of difficulties. Specifically, users who place excess traffic on the network can have a negative impact on the performance of users who do not place excessive traffic on the network. Additionally, PVCs with excess traffic can easily become problem PVCs with poor performance. Therefore, it is important that PVCs adhere to their contracted rate to avoid network traffic congestion.
Unfortunately, it has become apparent that a number of the PVCs on various networks are using more than their allotted portion of network resources. While carriers should support the ability of customers to burst to the access rate, there comes a time when PVC utilization is excessive. Consequently, it would be advantageous to identify PVCs that make excessive use of the network and estimate a new CIR for each of those circuits. This will provide fairness among all PVC circuits connected to the network and will provide accurate information for network traffic engineering estimations.
Therefore, there exists a need in the art for a method of calculating a new CIR for a PVC when the traffic has grown to a point that exceeds the contracted capacity of the PVC.